Multi-band lookup table type predistorter

Abstract

A lookup table type predistorter for reading out distortion compensation data by using a difference signal between a power amplifier input signal and an output signal as a reference signal; wherein N input side variable band signal extractors extract transmitting signals in N frequency bands from the input signal, N output side variable band signal extractors extract signals in N frequency bands from the output of power amplifier, and N difference detectors detect differences between N frequency band signals respectively detected at the input side and the output side as N reference signals, which are used to read out N compensation data from N lookup tables, the N compensation data are added to the transmitting signals in N frequency bands, and N results of addition are combined to produce an output of the predistorter.

1. A multi-band lookup table type predistorter for adding predistortion components for canceling distortion components produced by a power amplifier to an input transmitting signal and outputting the result comprising:
 N output side variable band signal extractors for extracting output signals in N frequency bands from output signals from the power amplifier, wherein the N frequency bands are variable and N is an integer of 2 or greater; 
 N difference detectors for detecting differences between transmitting signals in N frequency bands and N output signals from said N output side variable band signal extractors; 
 N lookup tables for reading distortion compensation data of corresponding N frequency bands by using differences of said N frequency bands as reference signals; 
 N adders for adding the distortion compensation data read out from said N lookup tables to the transmitting signals in the corresponding N frequency bands; 
 a combiner for combining the added outputs from said N adders and outputting the combined result as a transmitting signal with the predistortion; and 
 a frequency band controller for controlling said N frequency bands of said N output side variable band signal extractors. 
 
     
     
       2. The predistorter according to  claim 1 , further comprising N input side variable band signal extractors for extracting transmitting signals in said N frequency bands from the input transmitting signal in response to receiving a band control common to said N output side variable band signal extractors from said frequency band controller. 
     
     
       3. The predistorter according to  claim 2 , wherein at least said N input side variable band signal extractors, said N output side variable band signal extractors, said N difference detector, and said N adders are realized by an analog signal processing circuit. 
     
     
       4. The predistorter according to  claim 2 , wherein at least said N input side variable band signal extractors, said N output side variable band signal extractors, said N difference detectors, and said N adders are realized by a digital signal processing circuit. 
     
     
       5. The predistorter according to  claim 2 , wherein at least either of said N input side variable band signal extractors and said N output side variable band signal extractors consist of band elimination filters with a plurality of different eliminating bands. 
     
     
       6. The predistorter according to  claim 2 , wherein at least either of said N input side variable band signal extractors and said N output side variable band signal extractors consist of N pass-band filters with the center frequencies of respective frequency bands. 
     
     
       7. The predistorter according to  claim 2 , wherein said frequency band controller controls the center frequencies of said N input side variable band signal extractors and said N output side variable band signal extractors. 
     
     
       8. The predistorter according to  claim 2 , wherein said frequency band controller controls the bandwidths of said N input side variable band signal extractors and said N output side variable band signal extractors. 
     
     
       9. The predistorter according to  claim 2 , further comprising an update controller for updating compensation data of said N lookup tables based on differences of said N frequency bands. 
     
     
       10. The predistorter according to  claim 2 , wherein said frequency band controller comprises a frequency band detector for detecting signals of N frequency bands from said input transmitting signal, and a band setting unit for controlling said N input side variable band signal extractors and said N output side variable band signal extractors based on said detected signals of the N frequency bands.